Vasoconstrictor reserve and sympathetic neural control of orthostasis
Vasoconstrictor reserve and sympathetic neural control of orthostasis
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DOI：
10.1161/01.cir.0000146384.91715.b5
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发表时间：
2004-11-02
期刊：
影响因子：
37.8
通讯作者：
Levine, BD
中科院分区：
文献类型：
--
作者：
Fu, Q;Witkowski, S;Levine, BD
背景-我们测试的假设，个体差异立位耐力是依赖于程度的神经和血管储备vasoconstriction.Methods和结果-肌肉交感神经活动（MSNA）和血流动力学测定在12名健康的年轻志愿者在60度头向上倾斜（HUT），其次是冷加压试验（CPT）在HUT。立位耐力测定采用渐进式下体负压（LBNP）至晕厥前期。在正常血容量和低血容量条件下随机进行相同的方案。HUT时平均动脉压升高，每搏输出量减少，心率、MSNA和总外周阻力增加（均P <0.01）。在HUT中应用CPT并未进一步增加HR或降低每搏输出量，但在某些受试者中，平均动脉压升高（P <0.01），MSNA和TPR增加。在两种情况下，从-50 mmHg LBNP（相当于单独60度HUT）到晕厥前期的时间与CPT产生的MSNA变化呈正相关（r = 0.442，P = 0.039）。MSNA升高越多，CPT时TPR升高越多，至晕厥先兆时间越长（均P <0.05）。一个主题有显着增加MSNA，但小的增加TPR在CPT期间，这表明交感神经活性和外周血管resistance.Conclusions增加之间的脱节-这些结果支持我们的假设，并表明血管收缩能力是一个贡献者直立耐受在人类。因此，血管收缩储备可能是立位不耐受个体差异的一种机制。
Background - We tested the hypothesis that individual variability in orthostatic tolerance is dependent on the degree of neural and vasomotor reserve available for vasoconstriction.Methods and Results - Muscle sympathetic nerve activity (MSNA) and hemodynamics were measured in 12 healthy young volunteers during 60degrees head-up tilt ( HUT), followed by a cold pressor test (CPT) in HUT. Orthostatic tolerance was determined by progressive lower-body negative pressure ( LBNP) to presyncope. The same protocols were performed randomly in normovolemic and hypovolemic conditions. We found that mean arterial pressure increased and stroke volume decreased, whereas heart rate (HR), MSNA, and total peripheral resistance (TPR) increased during HUT ( all P < 0.01). Application of the CPT in HUT did not increase HR or decrease stroke volume further but elevated mean arterial pressure ( P < 0.01) and increased MSNA and TPR in some subjects. There was a positive correlation between the time to presyncope from - 50 mm Hg LBNP ( equivalent to 60degrees HUT alone) and the changes in MSNA produced by the CPT under both conditions ( r = 0.442, P = 0.039). Those who had greater increases in MSNA had greater increases in TPR during the CPT and longer time to presyncope ( both P < 0.05). One subject had dramatic increases in MSNA but small increases in TPR during the CPT, which indicates a disassociation between sympathetic activity and the increase in peripheral vascular resistance.Conclusions - These results support our hypothesis and suggest that vasoconstrictor capability is a contributor to orthostatic tolerance in humans. Vasoconstrictor reserve therefore may be one mechanism underlying individual variability in orthostatic intolerance.